The present invention relates to a method for cutting a continuous glass sheet during the production of flat glass with an inhomogeneous thickness distribution across its width by moving a cutting tool at an angle to the direction of travel across the width of the glass sheet with a cutting force predetermined by a controller, producing a fissure, then mechanically breaking the glass sheet along the fissure.
Flat glass, in contrast to hollow glass ware, is understood to mean all glasses manufactured with a flat shape, independent of the production technology used.
In addition to the float glass process, various down-draw methods are used today to manufacture flat glasses, such as overflow fusion, redraw and nozzle processes, and various up-draw processes, such as the Fourcault or Asahi process, for shaping. The glass is shaped into a glass sheet while it is still in a viscous state due to the high operating temperatures. The glass sheet is then cooled, whereby the temperature of the glass passes the two annealing points and then cools to essentially room temperature.
The continuously-produced glass sheet is subsequently cut into panels in various final and intermediate formats in a cross-cutting machine at an angle to the direction of flow. To this end strain states induced by a mechanical small cutting wheel or thermally induced, e.g., using a laser beam are typically used to produce a rupture in the glass surface, i.e., a crack or notch, which is continued across the width of the sheet; subsequently, the microscopically small fissure that results or was continued across the width of the sheet is driven through, using external forces, until it reaches the other side and the glass sheet is divided into separate pieces.
During the shaping of the glass sheet, a somewhat different thickness distribution usually forms on the edges than in the center or net-usable-surface area due to surface forces, temperature and viscosity gradients and also as a result of the action of mechanical shaping and conveyance tools, such as rollers. The thickness in the edge regions can become smaller than in the net-usable-surface area, as is the case with the nozzle process using the down-draw method, or larger than in the net surface area, as is the case with the float glass process. The edge region on either side of the glass sheet is referred to as the border region.
This inhomogeneous thickness distribution across the width of the glass sheet becomes noticeable during production of thin glass (<3 mm) in particular.
During cross-cutting, depending on the system, a small cutting wheel is typically moved across the glass surface with pressure, with the objective of mechanically creating a notch (fissure) across the entire width of the glass sheet. The glass sheet is not divided into separate pieces yet, however. The glass sheet is broken at the fissured point in a further working step.
With the known systems, the cutting force with which the cross-cutting of the particular glass sheet is carried out is set at a constant value by the operator of the cross-cutting machine in the associated electrical controller. If the cross-cutting procedure is then carried out using a cutting force with a constant setting, the following two states result:                1. The cutting force is set at a level that enables an adequate surface notch to be created in the thicker regions, and breaking can then be carried out successfully. In the thin regions of the glass sheet, the glass is acted upon with excessive cutting force. As a result, the glass is broken into pieces in an uncontrolled manner, before the actual breaking process can be carried out.        2. The cutting force is set at a level that enables an adequate surface notch to be created in the thin regions, and the glass remains intact. An inadequate notch is created in the thicker regions and, above all, the roller tracks, however. In the subsequent breaking procedure, the borders are therefore either not broken or are broken in an uncontrolled manner.        
In either case, as a result of the uncontrolled breaking, the net glass separated from the border region cannot be used, or it can be used only if additional work is performed.
The same applies for cross-cutting using thermally induced strain states, e.g., using a laser beam with a constant output, combined with a mechanical starting point of a fracture created using a cutting tool.